Rotor and contact assembly for variable resistance device

ABSTRACT

In a variable resistance device of the type including a housing enclosing an annular resistance element, a rotor member mounted within the housing, an electrically conductive wiper contact attached to the rotor member for rotation therewith, the wiper contact having a resilient wiper arm extending into electrically conductive engagement with the resistance element, and drive means for rotating the rotor member, the improvement wherein the rotor member includes a pocketlike slot therein, and wherein the wiper contact includes a substantially planar section, the width of at least a portion of which is slightly greater than the width of the slot, the planar section extending into the slot thereby forming an interference fit therewith. The wiper contact includes an upended tab which abuts against a wall of the rotor member to accurately locate the contact relative to the rotor member. A tab on the wiper contact extends through a further slot in the rotor member into a cavity therein. By bending the tab down into the cavity, the contact is securely locked in place.

United States Patent [72] Inventor George A. Gerstmeier Santa Ana, Calif. [21] Appl. No. 18,835 [22] Filed Mar. 12,1970 [45] Patented Nov. 2,1971 [73] Assignee Beckman Instruments, Inc.

[54] ROTOR AND CONTACT ASSEMBLY FOR VARIABLE RESISTANCE DEVICE 11 Claims, 11 Drawing Figs.

[52] US. Cl 338/174, 338/202, 339/221 R [51] Int. Cl 1101c 9/02 [50] Field of Search 338/160,

162,170,174, 202,D1G. 1; 339/221; 200/1 1 A [56] References Cited UNITED STATES PATENTS 2,495,623 l/1950 Benander 339/221 X 3,124,778 3/1964 Youngbeck... 338/D1G. 1 3,124,780 3/1964 Hulbert 338/202 X 3,217,285 11/1965 Barre 339/221 X 3,369,208 2/1968 Kirkendall 338/174 3,378,803 4/1968 Yungblut 338/174 Assistant Examiner-Gerald P. Tolin Attorneys-Ferd L. Mehlhoff and Robert J. Steinmeyer ABSTRACT: In a variable resistance device of the type including a housing enclosing an annular resistance element, a rotor member mounted within the housing, an electrically conductive wiper contact attached to the rotor member for rotation therewith, the wiper contact having a resilient wiper arm extending into electrically conductive engagement with the resistance element, and drive means for rotating the rotor member, the improvement wherein the rotor member includes a pocketlike slot therein, and wherein the wiper contact includes a substantially planar section, the width of at least a portion of which is slightly greater than the width of the slot, the planar section extending into the slot thereby forming an interference fit therewith. The wiper contact includes an upended tab which abuts against a wall of the rotor member to accurately locate the contact relative to the rotor member. A tab on the wiper contact extends through a further slot in the rotor member into a cavity therein. By bending the tab down into the cavity, the contact is securely locked in place.

PATENTEMnvz IQTI 3317-878 sum 2 [1F 2 v INVENTOR. 7/ 650/765 ,4. GIRSTME/ER A TORNEY ROTOR AND CONTACT ASSEMBLY FOR VARIABLE RESISTANCE DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotor and contact assembly for a variable resistance device and, more particularly to a method and means for rigidly and accurately securing an electrically conductive wiper contact to the rotor member of a variable resistance device.

2. Description of the Prior Art The apparatus of the present invention is particularly applicable to miniature potentiometers of the type which include a housing enclosing an annular variable resistance element, a rotor member mounted within the housing in spaced, juxtaposed relation with respect to the resistance element, an electrically conductive wiper contact attached to the rotor for rotation therewith and appropriate terminals for connecting the resistance element and the wiper contact with an external electrical circuit. Such miniature potentiometers are often used in electrical circuits in which accuracy and precision are requirements. Therefore, the position of the rotor member must accurately define the point of contact between the wiper contact and the resistance element and the wiper contact must accurately follow the motion of the rotor member. The first requirement is guaranteed by providing a mounting arrangement which allows high precision in positioning the wiper contact on the rotor member. The second requirement is quaranteed by providing a method and means for securely and rigidly attaching the wiper contact to the rotor member so that the contact maintains continuity with the resistance element and closely follows the motion of the rotor member under the most severe conditions.

Substantial difficulties have been encountered in satisfying these requirements in the case of very small potentiometers since most conventional attaching methods which are capable of high accuracy are relatively large. Therefore, it is common practice to attach the wiper contact to the rotor member by cementing or riveting. However, when cementing or riveting any two parts together, it is usually difficult to accurately position one member relative to the other. In addition, the resulting union is often insecure. This is quite unacceptable in the case of a potentiometer since the contact could, under severe conditions, break loose of the rotor member.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a method and means for attaching an electrically conductive wiper contact to a rotor member which substantially overcomes these disadvantages of the prior art. The present attaching technique provides a mounting arrangement which allows great accuracy in positioning the wiper contact on the rotor member. In addition, such accuracy is achieved with a mounting arrangement which is very simple to assemble without the requirement for additional parts other than the wiper contact and the rotor member. Once assembled, the wiper contact is rigidly secured to the rotor member so that relative movement between the parts is essentially impossible. Finally, the present mounting arrangement assures the maintenance of continuity between the wiper contact and the resistance element under the most severe conditions.

Briefly, the present method and means for attaching a wiper contact to a rotor member utilizes an interference fit between the respective parts to accurately position and firmly attach the wiper contact relative to the rotor member. The rotor member includes a pocketlike slot therein, the slot extending in a direction parallel to the resistance element. The wiper contact includes a substantially planar section, the planar section extending into the slot in the rotor member. By making the width of at least a portion of the planar section of the wiper contact slightly greater than the width of the slot and relying on the inherent resiliency of the rotor material, the wiper contact may be slid into the slot in the rotor member to form a tight interference fit therebetween. The wiper contact includes an upended tab which abuts against a wall of the rotor member to accurately locate the contact relative to the rotor member. A tab on the contact extends through a further slot in the rotor member into a cavity therein. By bending the tab down into the cavity, the contact is securely locked in place.

It is therefore an object of the present invention to provide an improved method and means for attaching a wiper contact to a rotor member.

It is a further object of the present invention to provide a rotor mounted contact with maintains continuity with a resistance element or other medium under the most severe conditions.

It is a still further object of the present invention to provide a mounting arrangement for a rotor and contact assembly which allows great accuracy in positioning the contact on the rotor.

It is another object of the present invention to provide a method and means of attaching a wiper contact to a rotor which is very simple to assemble.

It is still another object of the present invention to provide an inexpensive arrangement for attaching a wiper contact to a rotor member which requires no additional parts other than the contact and the rotor.

Another object of the present invention is the provision of a rotor to which a wiper contact may be firmly attached, thereby eliminating side play and assuring good setability of the variable resistance element.

BRIEF DESCRIPTION OF THE DRAWINGS Still other objects, features and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of the preferred embodiment constructed in accordance therewith, taking in conjunction with the accompanying drawings wherein like numerals designate like parts in the several figures and wherein:

FIG. 1 is an isometric view of a preferred embodiment of rotor member constructed in accordance with the teachings of the present invention.

FIG. 2 is a top plan view of the rotor member of FIG. 1;

FIG. 3 is a left side elevation view of the rotor of FIG. 2;

FIG. 4 is a right side elevation view of the rotor of FIG. 2;

FIG. 5 is a bottom plan view of the rotor member of FIGS. 14;

FIGS. 6 and 7 are sectional views taken along the lines 6-6 and 7-7, respectively, in FIG. 2;

FIG. 8 is a top plan view of a wiper contact for use with the rotor member of FIGS. 1-7;

FIG. 9 is a front elevation view of the wiper contact of FIG.

FIG. 10 is an isometric view of the rotor member of FIGS.

1-7 with the wiper contact of FIGS. 8 and 9 connected DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and, more particularly, to FIGS. 1-7 thereof, there is shown a rotor member, generally designated 10, for use in a variable resistance device of the type generally referred to as a trimming" potentiometer. One type of trimming potentiometer with which rotor 10 may be used is fully disclosed in US. Pat. No. 3,378,803 issued to Charles W. Yungblut et al. and assigned to Beckman Instruments, Inc., the assignee of the present invention.

Rotor I0 is a generally disc-shaped element which may be molded of an insulative material such as glass-filled nylon or the like. Rotor 10 has a pocketlike slot 1 therein adjacent to the top surface thereof. Slot 1 is generally rectangular in shape, having parallel sidewalls 2 and 3, and an end wall 4, the

other end of slot 1 being open for insertion of the wiper contact. Slot 1 is partially enclosed at the top thereof by a generally U-shaped web 5. End wall 4 of slot 1 has a slot 6 therein, slot 6 leading into a cavity 7 in the rotor member 10.

Referring now primarily to FIGS. 8 and 9, there is shown a wiper contact, generally designated 20, for use with rotor member 10. Wiper contact 20 includes a thin, substantially planar section 21 having parallel side edges 22 and 23. Planar section 21 is adapted to extend into slot 1 in rotor member 10. The width of planar section 21, from edge 22 to edge 23, should be slightly greater than the width of slot 1 from sidewall 2 to sidewall 3 thereof. By way of example, if the overall diameter of rotor 10 is approximately one-quarter inch, the width of slot 1, between sidewalls 2 and 3, may be 0.1 l7i0.002 inches whereas the width of contact 20, between edges 22 and 23, may be 012010.001 inches. Therefore, when wiper contact 20 is inserted into slot 1 in rotor member 10, a holding force is provided by the interference between side edges 22 and 23 of contact 20 and sidewalls 2 and 3 of slot 1. Using the dimensions given previously, the depth of slot 1, between the body of rotor member 10 and webs 5, may be 0.0045 inch whereas the thickness of wiper contact 20 may be 0.003 inch. In this manner, a slight bowing of wiper contact 20 is permitted on insertion into slot 1 so that wiper contact 20 does, in fact, occupy the entire depth of slot 1.

Sidewalls 2 and 3 of slot 1 and edges 22 and 23 of planar section 21 may be linear throughout the lengths of slot 1 and wiper contact 20. Alternatively, and as shown in the embodiment of FIGS. 1-9, slot 1 and planar section 21 may be divided into two portions, the portions closest to wall 4 of slot 1 having smaller widths than the portions closest to the open end of slot 1. In the latter case, wiper contact 20 may be partially inserted into slot 1 before interferring contact is made between edges 22 and 23 of contact 20 and sidewalls 2 and 3 of slot 1. This simply serves to facilitate the insertion of wiper contact 20 into slot 1 and prevents damage of contact 20.

Wiper contact 20 may be stamped, etched or otherwise fabricated of a metal alloy such as beryllium-copper alloy, or any other suitable conductive material having appropriate spring characteristics.

Wiper contact 20 includes an upended tab 24 which extends from planar section 21 in a direction perpendicular thereto and an additional tab 25 which extends from front edge 29 thereof, tab 25 being coplanar with planar section 21.

As shown most clearly in FIG. 10, wiper contact 20 is inserted into slot 1 in rotor member 10 until tab 24 abuts against and edge 8 of web 5, thereby fixing the position of contact 20 relative to rotor member 10. With wiper contact 20 so positioned, tab 25 extends through slot 6 in end wall 4 into cavity 7. By bending tab 25 downwardly into cavity 7, contact 20 is locked in place.

Wiper contact 20 is provided with one or more resilient wiper arms 26 which extend upwardly from planar section 21 and which are adapted to contact the variable resistance element of a trimming potentiometer during rotation of rotor member 10, as will be explained more fully hereinafter. A further wiper arm 27 extends upwardly from a central portion of planar section 21 of wiper contact 20, wiper arm 27 adapted to contact the collector element of such trimming potentiometer.

With wiper contact 20 locked in place in rotor member 10, side webs partially overlap contact 20 and lend support thereto. This support is especially important at the fulcrum point, generally designated by the numeral 28 in FIG. 8, between wiper arms 26 and planar section 21 of wiper contact 20 as this allows wiper arms 26 to exert full force when deflected.

Referring now to FIG. 11, the assembled rotor member and wiper contact may be used in a trimming potentiometer, generally designated 30, of the type described in the beforementioned US. Pat. No. 3,378,803. For the purpose of fully understanding the present invention, a brief description of such potentiometer will be included. More specifically,

trimming potentiometer 30 may include a housing 31 of generally rectangular shape having at least one end wall 32 and sidewalls 33 defining a cavity 34. Within the open end of housing 31 is positioned a nonconductive base 45 having mounted thereon an annular-shaped resistance element 35 and an electrically conductive collector element 36. In the illustrated embodiment, there are three terminals, designated by reference numerals 37, employed to connect the opposite ends of resistance element 35 and collector element 36 to an external electrical circuit.

In order to mount rotor member 10 in cavity 34 for rotational movement about an axis substantially conforming to the axis of annular resistance element 35, rotor member 10 is provided with an axially disposed bearing recess 12 adapted to receive a bearing post 38 which projects into cavity 34 from end wall 32 of housing 31. Bearing post 38 and recess 12 position rotor member 10 within cavity 34 and permit rotational motion thereof about the axis of post 38.

As shown most clearly in FIGS. 1-4 and 10, rotor member 10 includes a raised, arcuately shaped pressure ring 11 which is located on side webs 5 and made integral therewith. When rotor member 10 is assembled in trimming potentiometer 30, as shown in FIG. 11, pressure ring 11 is slideably pressed against base member 45. The pressure on ring 11 is transmitting to web 5 to help retain contact 20 in slot 1.

As described in the beforementioned patent, trimmer potentiometer 30 may include stop means in order to prevent rotation of wiper contact 20 around a 360 rotational path. Such stop means may comprise a shoulder abutment 40 extending outwardly from sidewall 33 of housing 31 and adapted to engage with a stop extension 13 which protrudes radially from the periphery of rotor member 10.

A clutch mechanism may be employed in cooperation with rotor member 10, such clutch mechanism being identical to that described in the beforementioned U.S. Pat. No. 3,378,803. However, such a clutch mechanism is in no way essential to the operation of the present invention. For the purposes of completing the present disclosure and illustrating the operation of rotor member 10, rotor member 10 may include a plurality of radially oriented grooves or slots 14 in the back surface thereof which are engaged by projections 41 from a bowed clutch spring 42 which revolves around bearing post 38. Clutch spring 42 is driven by a gear 43 with is actuated by a worm 44. Thus, when worm 44 is rotated and clutch spring 42 moves, projections 41 in rotor grooves 14 cause rotor 10 to turn. When rotor 10 turns, wiper contact 20 moves with it. When stop extension 13 on rotor member 10 abuts against the side of shoulder 40 on housing 31, the spring projections 41 slip from one groove 14 to another and the travel of wiper contact 20 is limited. During such rotation, however, wiper arms 26 move along annular resistance element 35. The signal picked off by wiper arms 26 is electrically conducted via wiper arm 27 to collector element 36.

It can therefore be seen that in accordance with the present invention, there is provided a method and means for attaching an electrically conductive wiper contact to a rotor member which substantially overcomes the disadvantages previously encountered in the prior art. The present attaching technique provides a mounting arrangement which allows great accuracy in positioning wiper contact 20 on rotor member 10. In addition, such accuracy is achieved with a mounting arrangement which is very simple to assemble without the requirement for additional parts other than the contact and the rotor member. Once assembled, wiper contact 20 is rigidly secured to rotor member 10 so that no relative movement between the parts is permissible. This accuracy and rigidity is achieved through the interference fit between side edges 22 and 23 of wiper contact 20 and sidewalls 2 and 3 of slot 1 in rotor member 10. Accurate alignment is guaranteed through the operation of upended tab 24 which abuts against edge 8 of web 5. Furthermore, by the simple expedient of bending tab 25 into cavity 7, contact 20 is locked in place. Finally, when rotor member 10 is assembled in trimming potentiometer 30, pressure ring 11 is slideably pressed against base member 45, thereby adding pressure to webs 5 to help retain the position of contact 20.

While the invention has been described with respect to a preferred physical embodiment constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications and improvements may be made without departing from the scope and spirit of the invention.

Iclaim:

1. In a variable resistance device of the type including a housing enclosing a cavity in which an annular resistance element is supported on a nonconductive base member, a rotor member mounted within said housing, an electrically conductive wiper contact attached to said rotor member for rotation therewith, said wiper contact having a resilient wiper arm extending into electrically conductive engagement with said resistance element, and drive means for rotating said rotor member, the improvement wherein said rotor member includes a pocketlike slot having an opening normal to the axis of rotation of said rotor, a thin web partially enclosing said slot having an edge substantially perpendicular to said opening into said slot, and wherein said wiper contact includes a planar section having a tab extending upwardly from said planar section substantially perpendicular thereto, said planar section extending into said slot in said rotor member with said upstanding tab abutting against the edge of said web, and the width of at least a portion of said planar section of said wiper contact being at least as great as the width of said slot.

2. In a variable resistance device according to claim 1, the improvement wherein said slot has an end wall, said end wall having a second slot therein, and wherein said wiper contact includes a second tab extending through said second slot and bent over perpendicular to said wiper contact against said rotor to lock said wiper contact to said rotor member.

3. In a variable resistance device according to claim 1, the improvement wherein said rotor member includes a raised, arcuately shaped pressure ring positioned on said web, said pressure ring slideably engaging the base member adjacent said resistance element.

4. In a variable resistance device according to claim 1, the improvement wherein the width of at least a portion of said planar section of said wiper contact is slightly greater than the width of said slot.

5. In a variable resistance device according to claim 1, the improvement wherein said slot is generally rectangular in shape having parallel sidewalls, and wherein said wiper contact has parallel side edges, said edges of said wiper contact contacting said sidewalls of said slot.

6. In a variable resistance device according to claim 5, the improvement wherein said slot has an end wall which extends between said sidewalls, said end wall having a second slot therein, and wherein said wiper contact includes a second tab extending through said second slot and bent over perpendicular to said wiper contact against said rotor to lock said wiper contact to said rotor member.

7. In a variable resistance device according to claim 5, the improvement wherein the depth of said slot is slightly greater than the thickness of said planar section of said wiper contact.

8. A rotor-contact assembly for a variable resistance device comprising:

a generally disc-shaped rotor member, said rotor member having a pocketlike slot therein extending in a direction perpendicular to the axis of rotation of said rotor member, said slot having a generally rectangular shape with parallel sidewalls and having an opening normal to the axis of rotation of said rotor, a thin web partially enclosing said slot and having an edge perpendicular to said opening in said slot; and

an electrically conductive wiper contact having a planar section and including a tab which extends upwardly from said planar section, said wiper contact having substantially parallel side edges and being positioned in said slot in said rotor member with said tab abutting against said edge of said web said side edges of said wi er contact contacting and forming an Interference fi with said sidewalls of said slot.

9. A rotor-contact assembly according to claim 8, wherein said slot has an end wall having a second slot therein; and wherein said wiper contact further includes:

a second tab which extends from the front edge thereof, said second tab extending through said second slot and bent over substantially perpendicular to said wiper contact against said rotor to lock said wiper contact to said rotor member.

10. A rotor-contact assembly according to claim 8, wherein the depth of said slot is slightly greater than the thickness of said planar section of said wiper contact.

11. A rotor-contact assembly according to claim 8, wherein said rotor member comprises:

a web which partially encloses said slot, said web contacting and supporting said wiper contact: and

a raised, arcuately shaped pressure ring positioned on said web. 

1. In a variable resistance device of the type including a housing enclosing a cavity in which an annular resistance element is supported on a nonconductive base member, a rotor member mounted within said housing, an electrically conductive wiper contact attached to said rotor member for rotation therewith, said wiper contact having a resilient wiper arm extending into electrically conductive engagement with said resistance element, and drive means for rotating said rotor member, the improvement wherein said rotor member includes a pocketlike slot having an opening normal to the axis of rotation of said rotor, a thin web partially enclosing said slot having an edge substantially perpendicular to said opening into said slot, and wherein said wiper contact includes a planar section having a tab extending upwardly from said planar section substantially perpendicular thereto, said planar section extending into said slot in said rotor member with said upstanding tab abutting against the edge of said web, and the width of at least a portion of said planar section of said wiper contact being at least as great as the width of said slot.
 2. In a variable resistance device according to claim 1, the improvement wherein said slot has an end wall, said end wall having a second slot therein, and wherein said wiper contact includes a second tab extending through said second slot and bent over perpendicular to said wiper contact against said rotor to lock said wiper contact to said rotor member.
 3. In a variablE resistance device according to claim 1, the improvement wherein said rotor member includes a raised, arcuately shaped pressure ring positioned on said web, said pressure ring slideably engaging the base member adjacent said resistance element.
 4. In a variable resistance device according to claim 1, the improvement wherein the width of at least a portion of said planar section of said wiper contact is slightly greater than the width of said slot.
 5. In a variable resistance device according to claim 1, the improvement wherein said slot is generally rectangular in shape having parallel sidewalls, and wherein said wiper contact has parallel side edges, said edges of said wiper contact contacting said sidewalls of said slot.
 6. In a variable resistance device according to claim 5, the improvement wherein said slot has an end wall which extends between said sidewalls, said end wall having a second slot therein, and wherein said wiper contact includes a second tab extending through said second slot and bent over perpendicular to said wiper contact against said rotor to lock said wiper contact to said rotor member.
 7. In a variable resistance device according to claim 5, the improvement wherein the depth of said slot is slightly greater than the thickness of said planar section of said wiper contact.
 8. A rotor-contact assembly for a variable resistance device comprising: a generally disc-shaped rotor member, said rotor member having a pocketlike slot therein extending in a direction perpendicular to the axis of rotation of said rotor member, said slot having a generally rectangular shape with parallel sidewalls and having an opening normal to the axis of rotation of said rotor, a thin web partially enclosing said slot and having an edge perpendicular to said opening in said slot; and an electrically conductive wiper contact having a planar section and including a tab which extends upwardly from said planar section, said wiper contact having substantially parallel side edges and being positioned in said slot in said rotor member with said tab abutting against said edge of said web, said side edges of said wiper contact contacting and forming an interference fit with said sidewalls of said slot.
 9. A rotor-contact assembly according to claim 8, wherein said slot has an end wall having a second slot therein; and wherein said wiper contact further includes: a second tab which extends from the front edge thereof, said second tab extending through said second slot and bent over substantially perpendicular to said wiper contact against said rotor to lock said wiper contact to said rotor member.
 10. A rotor-contact assembly according to claim 8, wherein the depth of said slot is slightly greater than the thickness of said planar section of said wiper contact.
 11. A rotor-contact assembly according to claim 8, wherein said rotor member comprises: a web which partially encloses said slot, said web contacting and supporting said wiper contact: and a raised, arcuately shaped pressure ring positioned on said web. 